Ali Nadernezhad

Multifunctional 3D printing of heterogeneous hydrogel structures.

Multimaterial additive manufacturing or three-dimensional (3D) printing of hydrogel structures provides the opportunity to engineer geometrically dependent functionalities. However, current fabrication methods are mostly limited to one type of material or only provide one type of functionality. In this paper, we report a novel method of multimaterial deposition of hydrogel structures based on an aspiration-on-demand protocol, in which the constitutive multimaterial segments of extruded filaments were first assembled in liquid state by sequential aspiration of inks into a glass capillary, followed by in situ gel formation. We printed different patterned objects with varying chemical, electrical, mechanical, and biological properties by tuning process and material related parameters, to demonstrate the abilities of this method in producing heterogeneous and multi-functional hydrogel structures. Our results show the potential of proposed method in producing heterogeneous objects with spatially controlled functionalities while preserving structural integrity at the switching interface between different segments. We anticipate that this method would introduce new opportunities in multimaterial additive manufacturing of hydrogels for diverse applications such as biosensors, flexible electronics, tissue engineering and organ printing.

Effect of Tricalcium Magnesium Silicate Coating on the Electrochemical and Biological Behavior of Ti-6Al-4V Alloys

In the current study, a sol-gel-synthesized tricalcium magnesium silicate powder was coated on Ti-6Al-4V alloys using plasma spray method. Composition of feed powder was evaluated by X-ray diffraction technique before and after the coating process. Scanning electron microscopy and atomic force microscopy were used to study the morphology of coated substrates. The corrosion behaviors of bare and coated Ti-6Al-4V alloys were examined using potentiodynamic polarization test and electrochemical impedance spectroscopy in stimulated body fluids. Moreover, bare and coated Ti-6Al-4V alloys were characterized in vitro by culturing osteoblast and mesenchymal stem cells for several days. Results demonstrated a meaningful improvement in the corrosion resistance of Ti-6Al-4V alloys coated with tricalcium magnesium silicate compared with the bare counterparts, by showing a decrease in corrosion current density from 1.84 μA/cm2 to 0.31 μA/cm2. Furthermore, the coating substantially improved the bioactivity of Ti-6Al-4Valloys. Our study on corrosion behavior and biological response of Ti-6Al-4V alloy coated by tricalcium magnesium silicate proved that the coating has considerably enhanced safety and applicability of Ti-6Al-4V alloys, suggesting its potential use in permanent implants and artificial joints.

Development of Bioink from Decellularized Tendon Extracellular Matrix for 3D Bioprinting

Using decellularized extracellular matrix (dECM) hydrogels as bioinks has been an important step forward for bioprinting of functional tissue constructs, considering their rich microenvironment and their high degree of biomimicry. However, directly using dECM hydrogels as bioinks may not be suitable for bioprinting processes because of the loss of shape fidelity and geometrical precision of bioprinted structure due to their slow gelation kinetics. In this article, the development and direct bioprinting of dECM hydrogel bioink from bovine Achilles tendon were presented. The developed bioink is used for a microcapillary-based bioprinting process without any support structure and/or any additional cross-linker components. The reported decellularization and solubilization methods yield dECM pre-gels which turn into stable hydrogels in a short time at physiological conditions. The gelation kinetics and mechanical strength of bioinks with different concentrations and digestion times are characterized. A support structure-free 3D bioprinting of the developed bioink is shown by aspirating dECM bioinks and then in situ gelation and extrusion through a fine microcapillary nozzle. The viability assays indicate that the developed dECM bioink has no cytotoxic effect on encapsulated NIH 3T3 cells and the cells show lineage-specific morphology in the early days of culture as well.

Nanosilicate embedded agarose hydrogels with improved bioactivity

This paper reports the synthesis of nanocomposite agarose hydrogels with improved bioactivity with the incorporation of anisotropic 2D nanosilicates (Laponite) to promote cell binding, growth and proliferation. Rheological measurements showed that the incorporation of nanosilicates slightly increased the gelation temperature (Tgel). The use of higher nanosilicate content at the constant agarose concentration improved the mechanical properties of the gels. Due to the non-swelling nature of agarose, the addition of nanosilicates did not result in any remarkable change in the swelling properties of the agarose gels, while collapsed agarose nanofibers were observed with the incorporation of nanosilicates. EDX analysis confirmed the presence of the embedded nanosilicates in the gel matrix. The existence of physical interactions between nanosilicate and agarose was demonstrated by FTIR over the shifting of SiO stretching band to a lower frequency. The encapsulated NIH/3T3 fibroblast cells showed enhanced proliferation and spreading in the presence of nanosilicates.

Effect of ball milling time on the synthesis of nanocrystalline merwinite via mechanical activation and heat treatment

Abstract Nanocrystalline merwinite was successfully synthesized by mechanical activation of a mixture of magnesium hydroxide, calcium oxide and silica gel powders followed by heat treatment. The phase development and various physical properties were investigated as a function of milling time using X-ray diffraction, scanning electron microscopy, simultaneous thermal analysis, particle size analysis and transmission electron microscopy. The results showed that formation of merwinite in annealed powders was enhanced by increasing the milling time. Nanocrystalline merwinite powder with an average crystallite size of about 36 nm was obtained after 30 hours of ball milling and subsequent annealing in 900 °C for 1 hour.